This relates to the fabrication of integrated circuit packages for holding integrated circuit chips.
In some integrated circuit packages, a substrate may mount one or more integrated circuit chips. Between the chip and the substrate may be an underfill material. Advantageously, this material fills up the region between the chip and the substrate, but does not extend outwardly by an excessive amount therefrom. Doing so may adversely affect the operation of the packaged part. For example, when the underfill material is injected between the integrated circuit and the substrate, it may tend to flow outwardly, creating what is called a tongue of material that extends out from under the integrated circuit die.
Underfilling may be done by capillary flow. In order to achieve high throughput times, the underfill may be made with a very low viscosity and good wettability to the substrate solder resist. Moreover, the underfill may be dispensed at elevated temperatures. The result of all these factors is that a tongue of underfill is left on the underfill dispense side of the package. The tongue effectively increases the footprint of the package.